LS2 report: Before the return of the cold

Since the start of January, the liquid helium flowing through the veins of the LHC's cooling system has gradually been removed the accelerator and, one by one, the eight sectors of the LHC have been brought back to room temperature. "It takes about four weeks to bring a single sector from its nominal temperature of 1.9 K (-271°C) back to room temperature," explains Krzysztof Brodzinski, an engineer working on the operation of the LHC's cryogenic system. At least 135 tonnes of helium are require...